I have a 400 pound safe in my basement. Me and my friend were able to get it from the bed of my truck, up to the front porch, and back down the basement steps with just a dolly and some careful manuvering. I would bet if you had 4 guys, getting it up a set of stairs wouldn't be that hard.
Mine is also a Stack-on brand, but it dosen't hold NEARLY the amount of guns it was supposed to. It would if a gun = a peice of pipe, but with things like pistol grips, cocking handles, and even just a stock, they're laying all over each other. I ended up just removing all the little cradles and placing all my guns in sleeves. It would be absolutely phyiscally impossible to fit as many guns as advertised in there without just dumping them in there, so if your collection is a growing one, I suggest you find an alternative.
If you're really worried that your room mate's friends are going to break into your locked safe you need to move. Sorry, but it's that simple. It's not something you could just casually do.
The Stack-on I bought seems to be built like a tank, but even it (or any others I've seen) wouldn't have a chance agaist a simple angle grinder.